1. Field of the Invention
This invention relates to improvements in a wheel speed sensor arrangement, and more particularly to an installation configuration of a wheel speed sensor for an automotive vehicle.
2. Description of the Prior Art
A wheel speed sensor for detecting the rotational speed of a road wheel of an automotive vehicle has been proposed as shown, for example, in Japanese Utility Model Provisional Publication No. 63-39677. This wheel speed sensor will be discussed with reference to FIG. 4 of the present application. The wheel speed sensor includes a sensor main body (magnetic pickup) 4 which is positioned in close proximity to the teeth 2a of a serrated sensor rotor (impulse ring) 2. The wheel speed sensor 4 is adapted to magnetically detect rotation of the sensor rotor 2.
The sensor main body 4 is fitted in an installation hole 6A of an installation member 6 under a so-called clearance fitting. The installation member 6 is, for example, fixedly connected to the base section of a suspension strut. The cylindrical section of the sensor main body 4 is usually made of stainless steel taking corrosion resistance into consideration, while installation member 6 is made of aluminum or aluminum alloy taking weight into consideration.
However, drawbacks have encountered in such a conventional arrangement of the wheel speed sensor, in which the aluminum-made installation member corrodes for the following reasons: aluminum has a much smaller electro-chemical potential (electromotive force) than stainless steel so that electrocorrosion or galvanic corrosion occurs in the aluminum it is in contact with the stainless steel under humid conditions during prolonged use. Simultaneously a natural corrosion or oxidation occurs in the aluminum. Such corrosions produce oxidation of aluminum as indicated by the reference character K in FIG. 4. The oxide K will press and crush (deform) the outer surface of the cylindrical section 4A of the sensor main body 4, thereby wrecking a magnetic pickup mechanism contained in the cylindrical section 4A.